Contemporary software and cognitive radio technologies have allowed regulators to transition from a scheme of allocation of radio frequencies by band having a specified usage such as commercial cellular, military radar, navigation aids, and satellite communications to one of shared spectrum. IEEE 802.11, WiFi, for example, shares the 5.9 GHz band with radar systems. A WiFi device detects the presence of the radar and then ceases to use that band for 30 minutes. The signal processing of a radio signal may determine that such a signal represents noise, a signal authorized to share such a band, or an incumbent signal to which a secondary user such as WiFi must defer by evacuating the band, or may in advanced spectrum sharing systems tolerate a given level of interference from such an incumbent. Contemporary technology typically classifies an incumbent signal into a specific type of incumbent signal such as a particular military radar, navigation signal (e.g. GPS), or a communications type of signal such as a fixed satellite station (FSS); this process is termed signal classification. Historically the collection of characteristics of military signals for the purpose of discovering their capabilities, limitations, and vulnerabilities has been called signals intelligence (SIGINT). For example, see the discussion of signals intelligence in Joint Publication 1-02, Department of Defense Dictionary of Military and Associated Terms (Washington, D.C.: The Pentagon) 31 Oct. 2009.
SIGINT has been dealt with via strict partitioning of the spectrum into bands with legal prohibitions on collecting signal information in the military bands. For example, Public Law Title 18 provides US espionage statues that prohibit the conduct of SIGINT by any private person or unauthorized party (e.g. an agent of a foreign government). Other countries with significant potential for adopting spectrum sharing technologies also have comparable legal prohibitions. Therefore the introduction of spectrum sharing would appear to require a commercial spectrum access system (SAS) to perform SIGINT in order to detect federal incumbent signals via a process of signal-type classification in order to infer that the specific interference encountered constitutes a specific federal or commercial (e.g. FSS) incumbent signal type.
In-band signal classification can be used by a given radio system having secondary use, e.g. of the 5.9 GHz radar band for wireless local area networking (WLAN), to determine whether interference (when present) is caused by an incumbent and can defer to the incumbent on its own. However, there are typically security risks to such an arrangement. For example, the classification of federal incumbent in-band interference with respect to specific signal type, such as a specific Naval radar system, may reveal its capabilities and limitations over time to an unauthorized party. For example, advanced persistent threat malware may access a SAS, thus realizing a de facto type of SIGINT for the operator of the malicious agent, such as an agent of a foreign government not amicable to the US (or other host nation). An additional disadvantage of in-band interference detection and classification is that a spectrum sharing radio device or a collection of many such devices must operate on the given frequency at the time of the interference in order to detect the interference, generating unintentional interference to the incumbent that could constitute jamming and that thus also could be subject to criminal sanctions.
Spectrum sharing occurs today. Some bands of licensed spectrum, such as the AWS spectrum band (1710 MHz), is licensed subject to exclusion zones where licensees cannot use the shared spectrum. For example, common carriers (e.g., Verizon, AT&T, etc.) are not allowed to use AWS spectrum within 80 miles of Cherry Point, N.C. because the FCC so stipulated in granting the relevant licenses. Currently, taking measurements to assure adherence to exclusion zones for spatial spectrum sharing is usually a tedious process. For example, network operators and major service providers (e.g., Verizon) take measurements by ordering a crew to drive an instrumentation van to the site in question in order to take measurements and to analyze the measurements (e.g., for network planning and management). Network operators and major service providers are often expected to protect such information regarding incumbent signals (e.g., acquired at Cherry Point) to avoid the potential for inadvertent SIGINT and unauthorized disclosure, which is potentially subject to legal sanctions. The industry refers to the cost of making such measurements, analyzing the signals, and protecting the results as drive time.
Contemporary wireless communication standards (e.g., LTE) empower handsets to report measurements to cellular infrastructure (e.g., such as eNode B (eNB) of a Verizon LTE wireless system). This allows such measurements to be used for network operations and planning functions without needing to drive a truck to measure signals in the area of interest. For example, the LTE term for this approach is termed minimizing drive testing (MDT) or as minimizing drive time (MDT). While beneficial, as spectrum sharing devices (e.g., such as small cells) proliferate, MDT from such cells may be employed by unauthorized third parties having malicious intent. For example, a third party can employing malware in contemplated SAS systems to exploit MDT without the service provider's knowledge or intent to perform SIGINT operations against a federal incumbent such as the US Navy. Similarly, for example, a future General Authorized Access (GAA) radio access point (RAP) may receive what appears to be noise in a vacant channel. A malicious agent may aggregate such measurements and could use the results of signal type classification in an attempt perform SIGINT against a federal incumbent.
Furthermore, it is often very tedious, and may not be legal, for a federal incumbent organization to provide all of the details of operation of a federal incumbent signal such as a military radar to a commercial SAS or service provider for signal type classification to use in order to avoid offering harmful interference to incumbent radar signals.